I have a 2005 zx4 with a 2.0 engine that is showing a PO193 code. The Fuel Rail Pressure Sensor has a 4 wire connector. With the Key on engine off and the connector unplugged from the sensor I am reading 5 volts on 3 of the connector sockets and 12 volts at ground when I switch the negative meter lead to battery positive. does anyone know how to test the sensor with a multi meter and were I can find a free wiring diagram for this car

I have changed the fuel filter and tested fuel pressure with a gauge just before the fuel rail it is 30 psi steady. Two days ago before I changed the filter, the fuel pressure would increase to 40 psi when I disconnected the vacuum line to the FRP sensor, now no change at all just a steady 30 psi. I don't believe changing the filter can be the problem. The only thing different now is that I have unplugged the connector from the sensor the connector was clean with no corrosion and I plugged it back in.

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Thanks for the reply. I received a good post from Member Marde and he stated that the 30 psi reading on a external physical gauge would be read as 40 psi if I had used a scan tool. I do not understand why the difference, however he stated that he has confirmed the difference on multiple tests. I found a post by member Lafilipczyk that you responded to that has decent info for testing the sensor with a meter. I will give it a try tomorrow.

Do you have any idea why the pressure would increase when I unplugged the vacuum line 2 days ago but now I get no change in pressure.

There is almost nobody or few active FF members here who have connected an external fuel pressure gauge for test purposes. Primary reason for this is that very few Foci have a factory schrader valve on the fuel rail; so most people test the system using only a scan tool. And even fewer people have done this while ALSO using a scan tool to see the (OBD data) fuel pressure reported. I am one of the few freaks who has done both of these simultaneously; using the external pressure gauge & using a scan tool that shows reported fuel pressure.

Your 30-psi on the external gauge is normal (especially during cooler weather, higher pressure should exist when warmer). The same pressure would be seen by the OBD data/scan tool as 40-psi. Ref my prior comments & same by Sailor.

Your DVM wiring tests seem to indicate that the system wiring is intact to/from the needed points. I recommend you replace the FRPS.

Quote:

Originally Posted by sailor

...If you aren't getting a change now when disconnecting the vacuum line you've either got no vacuum there, bad connection at the sensor, or bad sensor...

I think the OP/Arm Drag lost the 10-psi difference during his recent test because he has/had the FRPS electrically disconnected; so reconnecting/disconnecting the vac hose will not impact the system like he saw initially.

edit: also, as I stated in the other thread, I have not done exactly what the OP did, (disconnect the vac hose while watching FP on an external gauge) so I am unsure what the immediate resulting impact should be. Some of what I said is based on assumption, and a general understanding of what the system does/did during my testing a year+ ago.

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